Recently, expectations for industrial technology requiring high vacuum have been raised. For instance, energy saving has been strongly desired from the viewpoint of prevention of global warming, and energy saving of consumer electronics has been also an urgent issue. Especially, a thermal insulation apparatus such as a refrigerator, a freezer, or a vending machine requires a heat insulator having high heat insulation performance from the viewpoint of efficient use of heat.
As a general heat insulator, fiber material such as glass wool or foam such as urethane foam is used. However, for improving the heat insulation performance of the heat insulator, the heat insulator must be thinned. The heat insulator cannot be applied, when space capable of being filled with the heat insulator is restricted and space saving and effective use of the space are required.
As a heat insulator of high heat insulation performance, a vacuum heat insulator is proposed. This vacuum heat insulator is produced by inserting a core material serving as a spacer into a jacket material having gas barrier property, and by decompressing and sealing the inside.
The heat insulation performance can be increased by increasing the degree of vacuum inside the vacuum heat insulator, but gas existing inside the vacuum heat insulator is broadly classified into three following gases:                gas remaining without being exhausted in producing the vacuum heat insulator;        gas generated from the core material or jacket material after decompression and sealing (gas adsorbed by the core material or jacket material or reaction gas generated by reaction of an un-reacted component in the core material); and        gas coming from the outside through the jacket material.        
For adsorbing the gases, a method of filling a gas adsorbent into the vacuum heat insulator is provided.
For instance, Japanese Patent Unexamined Publication No. H09-512088 discloses a method of adsorbing the gas in the vacuum heat insulator using a Ba—Li alloy.
Of gases to be adsorbed by the gas adsorbent in the vacuum heat insulator, a hard-to-adsorb gas is nitrogen. That is because nitrogen molecules are non-polar molecules having a large binding energy of about 940 kJ/mol and hence are difficult to be activated. Therefore, using the Ba—Li alloy allows adsorption of nitrogen, and keeps the degree of vacuum of the inside of the vacuum heat insulator.
However, the gas adsorbent that is used for a conventional vacuum heat insulator and disclosed in Japanese Patent Unexamined Publication No. H09-512088 can be handled in an air atmosphere only for several minutes. This is described as “the gas adsorbent does not require heat treatment for activation, can absorb nitrogen even at normal temperature, and can be handled in an air atmosphere only for several minutes”. That is because handling in the air atmosphere for several minutes or longer exhausts the nitrogen adsorbing capability of the gas adsorbent in a producing step where the gas adsorbent comes into contact with air. As a result, air adsorbing capability for keeping the performance of the vacuum heat insulator including the gas adsorbent over time is reduced, and hence the performance degrades and performance fluctuation increases. For preventing the reduction of the nitrogen adsorbing capability of the gas adsorbent, the handling time in an air atmosphere is restricted to several minutes.
In the step of industrially producing the vacuum heat insulator using the gas adsorbent, however, it is desired that the gas adsorbent can be handled in an air atmosphere for a longer time. When the gas adsorbent is handled in the air atmosphere even for several minutes, some reduction of the nitrogen adsorbing capability is unavoidable.
The level of the activity of the gas adsorbent, namely time until the nitrogen adsorbing capability is saturated during leaving of the gas adsorbent in the atmosphere, depends on the form of the gas adsorbent and material specification. For example, when the gas adsorbent has a pellet shape, the nitrogen adsorbing capability is not saturated even when it is left in the atmosphere for a relatively long time. When the gas adsorbent is in powder form, the specific surface area becomes large and hence the nitrogen adsorbing capability is saturated only by being left in the atmosphere for a short time.
Therefore, when a powdery gas adsorbent that has an activity higher than that of Ba—Li is used, the contactable time with the atmosphere can be extremely reduced.
Recent growing of the demand of energy saving or the like has required higher heat insulation performance. For further increasing the degree of vacuum inside the vacuum heat insulator, it is desired to put the gas adsorbent of activity higher than that of Ba—Li to practical use. However, such a gas adsorbent of higher activity is difficult to be handled.